I think orks and nids are the only factions that would not ally.
Would the DW work temporarily with Orks to kill Tyranids?
DaedalRogue said:
Necrons will seek out great sources of life energy as they feed off of it. The Tyranids are their ultimate prize, being able to consume a hive fleet could reinvigorate an entire Necron tomb world, bring hundreds of thousands of soldiers back into action. Might even be enough to partially sate a C'Tan and bring up its strength to a frightening fighting potential.
So while the Tyranids would try to avoid or ignore Necrons - the reverse can't be said to be true. The Necrons will seek them out, as they seek out all life to consume it.
Not bad ideas but they don't mesh that well with new Necrons fluff. Since the C'tan are already sundered and the Necron Lords are awakening to retake the reins of the universe (and want to kill all the gods, all of them, but maybe not all living things...slaves are nice after all). The nids pose a great threat to the reawakening Necrons even having a galaxy to rule over. And there's been no retcon that nids no longer avoid Tomb Worlds. The Necrons have probably one of the better chances to turn the nid tide, assuming enough Tomb Worlds wake up and enough of the new Lords and their new Dynasties decide to ally against the threat to having a meaningful future.
How about the tyranids overpowering the weak and weird minds of the orks and turning them as mind drones on the marines?
you said they where inside a nid ship. means the hive minds power there is much more present than at a battlefield on a planet with just a tyrand and warriors as relay stations. so some orks could go nuts ( if that is altogether possible ) while others will become enslaved to the hive mind. ) the Tyrant than could walk off leaving the killteam to decide if theri going to waste time fighting the orks or persuing the tyrant.
Since i like giving players options on what to do this is a classic choice between weaker group of monsters or one hard bug to crack.
Just my thoughts thoug. Im surely going to use this encounter in one of my own chapters and see what happens.. i wonder...